Modified Atmosphere Packaging of Chicken Thigh Meat: Physicochemical and Sensory Characteristics during the Frozen Storage Period

This study aimed to explore the utilization of modiﬁed atmosphere packaging (MAP) for chicken thigh meat pieces (CTMP) during frozen storage periods (FSP) of 1, 30, 60, and 90 days at − 18 ° C. The treatments were divided into seven groups which are control, vacuum, 15% O 2 /15% N 2 /70% CO 2 , 30% N 2 /70% CO 2 , 50% O 2 /50% N 2 , 30% O 2 /70% CO 2 , and 1.5ml clove essential oil. The results showed that treatment of 30% N 2 /70% CO 2 was associated with a lower pH value than control. The pH, drip loss, TBA, peroxide number, and fatty acid percentage values were signiﬁcantly ( p < 0 . 05) increased as FSP rises. The eﬀect of the MAP and muscle ﬁber index (MFI) was signiﬁcantly diﬀerent ( p < 0 . 05) by the FSP. A decrease in the drip loss during storage and cooking when samples were treated with a MAP of 15% O 2 /15% N 2 /70% CO 2 , 30% N 2 /70% CO 2 , and clove oil groups were noted. The lowest values of TBA, peroxide number, and fatty acid percentage were recorded using 15% O 2 /15% N 2 /70% CO 2, 30% N 2 /70% CO 2 , and clove oil groups, respectively. There was an improvement in all sensory characteristics of all MAP and clove oil treatments.


Introduction
Fresh poultry meat is widely consumed due to its high nutritional value, while because of the chemical nature of meat, its products are subject to spoilage during storage [1,2]. Preserving the nutritional value of meat and extending its shelf life has aroused the interest of producers and consumers in the development and use of modern technologies in food processing and to secure the health aspect [3][4][5]. Among the effective factors on consumer acceptance, color is playing an important role in extending the market as a quality indicator. It is also an index of the freshness of the product [6]. Maintaining the desired color for a long time is one of the major hypotheses of new packaging ways [7,8]. It also has a significant effect on the meat appearance and acceptance of the way it is presented, which is one of the critical characteristics of the consumer [9][10][11].
MAP usually contains a mixture of gases, i.e., O 2 , which makes the color more stable, CO 2 , which inhibits microorganism's growth, and N 2 , which prevents deformation of the can shape [12][13][14]. MAP improves the meat quality, such as color [15,16], shelf life [17,18], and safety of meat [19]. MAP is one of the deactivation methods proposed for the inhibition of the growth of microorganisms in different food products [20]. MAP with CO 2 has a significant effect on microorganisms' development because CO 2 (under anaerobic conditions) is elevated during chilled storage, which encourages to lower growing lactic acid bacteria [21]. e current study is vital to manufacturing a simple device to apply MAP technology in meat packaging. Moreover, the previous studies [18,22,23] compared among MAP treatments, but in the current study, we compared among MAP treatments with di erent gases ratios and using essential oils, as well as control atmosphere packaging (using CO 2 and N 2 ). is study aimed to investigate the impact of MAP and FSP on the physical, chemical, and sensory properties of CTMP.

Chicken
igh Meat. In this study, 168-laying aged chicken ISA brown hens (G. gallus domesticus) were used. e birds were approximately 1.5 years old with a mean weight of 1.6 ± 0.21 kg. e birds were slaughtered manually, and after complete depletion for 150 seconds, the feathers and internal entrails were removed manually. en, the thighs were cut from carcass and stored at 4 ± 1°C in the refrigerator until further analysis. Totally, 84 CTMP was used in the experiments, one piece was put in every polyethylene pouch, and the air was discharged by using a vacuum lm sealing device (model FO2011, Hofer, German). After that, bags were treated as control, vacuum, 15% O 2 /15% N 2 /70% CO 2 , 30% N 2 /70% CO 2 , 50% O 2 /50% N 2 , 30% O 2 /70% CO 2 , and clove oil (1.5 ml) at various FSP (1, 30, 60, and 90 days) storage at −18°C. e treatments were replicated three times.

Modi ed Atmosphere
Packaging System. MAP system manufactured by Khalaf et al. [15] was used in the present study, as shown in Figure 1. At the beginning of the work, the delivery valves were installed on the packaging bags and punctured with a needle, and then they were lled with meat, emptied from the air, and closed tightly thermally. en, the envelope is placed on the sensitive scale and zeroed, and the charging tube is installed on the delivery valve. e valve of one of the gases is slowly opened and noticed the weight change, and until it reaches the required limit, it is stopped immediately, and so on for the rest of the gases; each experiment is repeated three times, and then, it is stored at 4 ± 1°C. e signi cant limitations of the proposed method are that the current application is limited to meat, and it needs to carry out for other meat types and fruits. Also, it needs special bags (provided with a small delivery valve) to control charging gases in the bags.

pH.
e method mentioned by AOAC [24] was followed using a pH meter (Lovibond Sensodirect pH 200, Germany), 5 g of minced CTMP was mixed with 100 ml of distilled water, put in a beaker, and then after ve min, the value of pH has been estimated.

Muscle Fiber Index (MFI)
. MFI was calculated depending on the procedure mentioned by Jeremiah and Martin [25]; where the frozen cubes of CTMP were jumbled with 50 ml of 0.25 M sucrose 0.02KCL solution. en, the pieces were stayed 5 min after thawing and crushed for 40 seconds at high strength and then ltered by a lter paper. e precipitate is taken and dried at 40°C temperature in an oven for 40 min, according to the following formula: MFI weight of the precipitate(g) × 100. (1)

Drip Loss (DL).
e meat sample was weighed, then tied with a thin cotton thread, placed in small nylon bags, and suspended in the refrigerator for 48 hours at 4°C. en, the sample was weighed after drying with the lter paper, and the drip loss was calculated as follows [26]: where W is the sample weight (g), PV is the PV (meq./kg oil), and N is the normality.

Free Fatty Acids (FFA)
. FFA was measured depending on the Nielsen et al. [28] method. 3 g of meat and 50 ml of ethyl alcohol at 98% concentration were added, then drops of phenolphthalein index were added to the sample after heating it in a water bath till boiling, and then cleared. 0.1 N KOH solution was added to the mixture until the color of the solution turned to light pink, and the following equation calculated the FFA: where A is the number of milliliters of KOH titrated with the oil or fat sample, B is the number of milliliters of KOH titrated with the plank sample, and 282 is the oleic acid molecular weight.

iobarbituric Acid (TBA).
e method of Nielsen et al. [28] has been used to determine the TBA value. 5 g of grounded meat was dissolved in 10 ml of CHCl 3 and put in a water bath for 5 minutes at a temperature of 60°C, and 10 ml of a 0.07% of TBA solution (in water mixed with the same volume of CH 3 COOH) was added up to it; then, the mixture was centrifuged (1000 rpm for five min), and then the suds were taken and placed in a boiling water bath for 30 minutes. e absorbance was measured at a wavelength of 532 nm at room temperature, and the TBA value was determined as mg of malonaldehyde MDA/kg oil. e concentration of malonaldehyde was calculated as follows: 2.8. Sensory Assessment. e meat (chicken thigh) was cut into small cubes, and then an electric oven was used at a temperature of 200°C for 15 minutes to grill meat. Ten expert panelists conducted the sensory evaluation who were chosen from the department of food sciences, the University of Basrah to evaluate the samples in color expression, tenderness, flavor, juiciness, and overall acceptance of chicken meat thighs using nine hedonic scales (1-9 scores) according to ISO8586-1 [29].

Statistical Analyses.
A factorial experiment with a completely random design (7 × 4) used seven types of modified atmosphere packaging (control, vacuum, 15% O 2 / 15% N 2 /70% CO 2 , 30% N 2 /70% CO 2 , 50% O 2 /50% N 2 , 70% CO 2 /30% O 2 , and oil of clove), and varied FSP (1-90 days) at −18°C with triplicate. e test has been utilized to contrast the treatment means at a significant level of 0.05, and the analysis was conducted using the SPSS program ver. 25. Table 1 presents the influence of the MAP and the FSP on the pH of CTMC. e results showed that the MAP and FSP have a significant (p < 0.05) influence on the pH value, where the pH value at 30% O 2 /70% CO 2 was 5.75 during the one-day FSP, where it reached 5.75 compared to the control treatment, which reached 5.88 in the same frozen storage period. While the pH value increased in the 90-day FSP for the same treatment, it reached 5.87 and 6.22, respectively, and the reason may be due to the low pH value of meat. Water, resulting in the formation of carbonic acid (−3HCO), causes slight acidity in meat [30]. erefore, it is observed that the pH values decreased at 15% O 2 /15% N 2 / 70% CO 2 , 30% O 2 /70% CO 2 , and 30% N 2 /70% CO 2 . Higher pH results in a darker color and high water tolerance; the texture is coarse and easy to spoil; lower pH results in dull color and lower water-bearing capacity; meat texture is tender. ere is a direct effect of the relationship between pH, water tolerance, and dark color, where high pH was observed in storage periods from 60 to 90 days due to water retention of meat, and this is consistent with Zakrys-Waliwander et al. [31] who illustrated that the meat pH decreased when the MAP was used in the medium. e pH value is related to the degree of color if it is dark or light. e high pH value of 5.8 or more increases the water holding capacity with a dark color and coarse building of the muscles, in addition, to provide suitable conditions for microbial corruption, either for the low pH value of 5.5 or fewer leads to the appearance of the transparent color, and the muscles are soft in structure with a prolonged storage period [32]. Nowak and Krysiak [33] indicated a decrease in the pH value after storage meat for a while in commercial MAP with a concentration of 60% CO 2 and 40% N 2 compared to storage meat in vacuum packaging. Table 2 shows the MAP and FSP on the MFI in the CTMP. e results showed that the MAP and the FSP have a significant (p < 0.05) effect on the MFI of CTMP, where the treatment of 30% N 2 /70% CO 2 at the one-day FSP gave the lowest value in MFI, which was 84.66 compared to the control. In the 90-day FSP, MFI reached 191.33. After 90 days of frozen storage period and using clove oil gave a lower MFI (93) at one day of FSP because of the antioxidant activity of clove oil. MFI was increased as FSP increased. When FSP increased from 1-90 days, the MFI increased from 106-170.66 using an MAP of 15% O 2 /15% N 2 /70% CO 2 , respectively. e lower value of MFI was 84.66 using an MAP of 70% CO 2 + 30% N 2 at one day of FSP. Denaturation of protein is determined depending on increasing MFI in the chilled and superchilled chicken breast meat during storage of myofibrils fragmentation is related to the degree of proteolysis during meat storage [34]. In vacuum packaging, MIF was increased from 108 to 176 when FSP increased from 1 to 90 days. To compare among treatments, control, vacuum, 30% N 2 /70% CO 2, 30% O 2 /70% CO 2 , 50% O 2 /50% N 2 , 15% O 2 /15% N 2 / 70% CO 2 , and clove oil were increased by 71.85, 64.76, 94.1, 47.67, 76, 61, and 74.9% when FSP increased from 1-90 days, respectively. Table 3 illustrates MAP and FSP on the drip loss of CTMP. e results showed significant (p < 0.05) differences in drip loss in meat treated by MAP during FSP. 30% N 2 /70% CO 2 , 30% O 2 /70% CO 2 , 15% O 2 /15% N 2 /70% CO 2 , 50% O 2 /50% N 2, and clove oil were given the lowest drip loss as it reached 3.33 3.12, 3.96, 3.54, and 3.46%, respectively, compared to the control treatment in one day of FSP. e vacuum treatment gave the highest drip loss and was very close to the control treatment in one day of FSP. High oxygen concentration is instrumental in water retention in meat, resulting in reduced drip loss during storage [35]. Drip loss in MAP-coated chicken meat was more than that of vacuum-packed [18].

Drip Loss.
e results illustrated that all treatments gave a significant increase (p < 0.05) in the drip loss during FSP, and the amount of drip loss was changed during FSP, with the highest value being in the 90 days of FSP in control (7.13%). At the same time, it reached to the lowest value at the FSP of one day at the treatment of 30% N 2 /70% CO 2 , which amounted to 32.1%. e frozen storage period negatively influences drip loss [30]. Drip loss depends on the amount of meat in the MAP package and storage time, and when storage time increased from 0 to 30 days, drip loss increased from 0 to 7.7%, respectively, using 100% CO 2 [36]. e amount of drip loss during storage and cooking is the amount of water bonding with meat muscle protein. e higher the amount of drip loss from the meat, the lower the nutritional value of the meat due to the loss of proteins, vitamins, and minerals [37]. Liquid loss using vacuum packaging was reduced by 3.43% compared to control, and the maximum reduction reached 33.04% using 70% CO 2 + 30% N 2 at 1 day of FSP. Little reduced liquid loss using vacuum packaging because of the pressure on meat led to the increased liquid loss.

Cooking Loos.
e impact of MAP and FSP on the cooking loss of CTMP is shown in Figure 2. Treatment of clove oil in the one day of FSP showed that the cooking loss was 13.31%, while the highest value of cooking loss reached 28.45 in the control treatment after 90 days of FSP. Cooking loss was increased as FSP increased for all treatments, i.e., when FSP was raised from 1 to 90 days, the cooking loss increased from 14.29 to 21.26%, respectively, using MAP of 15% O 2 /15% N 2 /70% CO 2 . ese results agree with Marcinkowska-Lesiak et al. [38], who showed that storage life is important and increases cooking loss. e increase in moisture loss during cooking with increasing storage period is a natural result of the increase in the content of exogenous enzymes [39]. e rate of moisture loss during cooking increases after 15 days of storage, and if muscle tissue storage progresses, the increase in moisture loss during cooking leads to a change in the structure of muscle protein [40]. ere is no signi cant di erence between vacuum packaging and control in cooking loss because vacuum generates lower pressure around the meat, extracting liquids from meat.

TBA.
e impact of MAP and FSP on the TBA value in CTMP is shown in Figure 3. e results showed that the FSP of 90 days for all MAP treatments showed a signi cant (p < 0.05) increase in the TBA compared to the rest of the FSP. It is also noted from the results that the lowest value of TBA was when using 15% O 2 /15% N 2 /70% CO 2 and vacuum treatment, which amounted to 0.27 and 0.26 mg MDA/kg, respectively, in the one day of FSP, while the highest value of TBA was in the 90 days of FSP. e results also showed that clove oil gave TBA values ranging between 0.31 and 0.65 mg MDA/kg for the FSP from 1 to 90 days. is indicates that the rancidity in this treatment is the lowest of all treatments. Dang et al. [18] con rmed that lipid oxidation in MAPcoated chicken breast llets was lower than in vacuum packs (0.47 versus 0.62 mg MDA/kg, respectively). Flaczyk et al. [41] reported that the smell and taste of rancid fat result from low-molecular-weight volatile substances such as ketones, aldehydes, or free fatty acids. e phenomenon of fat oxidation leads to undesirable changes that a ect its sensory qualities, such as color, texture, avor development, and   Journal of Food Quality smell. In addition, meat loses its quality of nutrition and health [42]. Antioxidant supplements can improve meat quality by modulating muscle metabolic processes, including enzymes, whose activity may also be a ected by packaging [43]. One of the leading causes of meat spoilage is the oxidation processes after converting muscle to meat or during meat processing and storage. However, the chemical changes responsible for turning muscle boil to meat lead to stopping the balance of the antioxidant body and thus facilitate the oxidation reactions of meat after slaughtering the animal [44]. Abdullah and Buchtová [45] treated chicken skin and wings by 80% O 2 + 20% CO 2 (MAP-O 2 ) and 70% N 2 + 30% CO 2 (MAP-N 2 ) and found that TBARS was increased with MAP-O 2 , and while MAP-N 2 increased, the shelf life of the product is increased. Figure 4 shows the e ect of MAP treatments and FSP on the peroxide value for CTMP. e results illustrated a signi cant (p < 0.05) e ect for the MAP and FSP on the peroxide value. e FSP of 90 days and the MAP treatment of 50% O 2 /50% N 2 presented the highest peroxide value, 2.30 meq/kg, compared to the MAP treatment of 30% N 2 /70% CO 2 at the one day of FSP, which was 1.24 meq/kg. e results illustrated no signi cant (p > 0.05) variation between the treatments of MAP, control, and clove oil in the one day of FSP. e results indicated signi cant variations (p < 0.05) between MAP treatments at 30 days of FSP, where the incline in the peroxide value was observed when using clove oil, which reached 1.80 meq/kg. e reason for the high peroxide value in control treatment may be due to chemical changes (oxidative rancidity) of fats as a result of the action of microorganisms that sort enzymes that break down fats, which in turn lead to fat oxidation and fatty acids formation as a result of the breakdown of the ester bonds between fatty acids and cholesterol. e formation of free radicals and the unsaturated bonds of fatty acids are the primary targets that free radicals cause oxidative stress, primarily linoleic and linolenic essential fatty acids [46]. e peroxide number, which expresses the oil content of peroxide compounds, was estimated by the reaction of saturated potassium iodide at room temperature (KI) in an acidic solution with oxygen bound in the form of peroxide in the oil, which will produce several iodine equivalents that are equivalent to the number of oxygen equivalents. It is most common in stored foods, including carcass meat. e shortchain fatty acids, aldehydes, and ketones are the products of the oxidation process and are responsible for the rancid avor in the meat. e value of the peroxide number ranges from 3-5 meq/kg, and the lower than this range, the more extended the storage period of the meat [47]. Figure 5 depicts the free fatty acids (FFA) vs. MAP treatments and FSP. e results showed that FAA signi cantly (p < 0.05) varied by MAP and FSP treatments, i.e., MAP treatment of 15% O 2 /15% N 2 /70% CO 2 and 50% O 2 /50% N 2 in one-day FSP reached 0.46 and 0.43%, respectively. e results revealed that using MAP treatments at 30 and 60 days of FSP gave a signi cant di erence (p < 0.05) in FFA compared to the control treatment, and it does not vary signi cantly (p > 0.05) over 90 days of FSP. As the storage period progresses, the increase in fatty acids in chicken leg meat may be due to a rise in the FFA content due to rancidity, a breakdown of the ester bond between fatty acids and cholesterol, and an increase in lipase activity [48]. e fat in meat contains a percentage of free fatty acids that increase in the incorrectly stored meat, which causes the fat to go rancid during storage as a result of its oxidation by atmospheric air or its hydrolysis by enzymes of microorganisms, which determine the age and quality of the fat in the meat. e lower the percentage of free fatty acids below 1.2, the lower the percentage of oxidation, thus increasing the shelf life of meat and improving its nutritional quality [47].    Figure 6(a) shows the MAP and the FSP on CTMP color. In terms of the interaction between MAP treatments and FSP, the results clari ed that the interaction e ect was signi cant (p < 0.05), as the treatment of 50% O 2 /50% N 2 and clove oil in the FSP for one day gave the highest value in color reached 7.60 and 7.71, respectively., while it appears from the Figure that the lowest value was in the vacuum treatment at 90 days of FSP, which amounted to 6.94, while it was in the control treatment in the same FSP, reached 6.77. When fats are oxidized, hydroperoxides enhance decomposition reactions [49]. Figure 6(b) illustrates the impact of MAP treatments and FSP on the juiciness of CTMP. e results presented that juiciness of chicken thighs meat treated by MAP of 15% O 2 / 15% N 2 /70% CO 2 and 30% O 2 /70% CO 2 at FSP of 1 day was signi cantly increased (p < 0.05) compared to the other treatments which reached 8.27 and 8.33, respectively, while in control and vacuum treatments were inclined to 6.88 and 6.77, respectively, at 90 days of FSP. Muscles stored in de ated casings gave a higher moisture loss during storage than muscles stored in casings (MAP) due to the pressure disturbance to which meat is exposed in vacated casings [35]. Figure 6(c) disclosed the in uence of MAP treatments and FSP in the tenderness of chicken thighs meat. Treatment of 15% O 2 /15% N 2 /70% CO 2 and clove oil at one day of FSP gave the highest values, which were 7.71 and 7.77, respectively, while the control and vacuum treatments have the lowest values, which were 6.88 and 6.44, respectively. is is because clove oil and CO 2 gas signi cantly impact meat tenderness. Figure 6(d) clari ed the in uence of MAP treatments and FSP on the avor of CTMP. e results showed that the treatments 15% O 2 /15% N 2 /70% CO 2 and clove oil gave a signi cant increase (p < 0.05) in the avor compared to the rest of the treatments, which amounted to 7.77 7.77, respectively, at the one day of FSP. e avor of CTMP by control and treated by vacuum treatments at 90 days of frozen storage period reached 6.71 and 6.49, respectively. e decrease in avor values may be due to the progression of storage periods, as the lengthening of the storage period a ects the volatile fatty acids that give avor to meat, while the MAP works to preserve the volatile fatty acids [50]. Figure 6(e) in uence of MAP treatments and FSP on the overall acceptance of chicken thigh meat. e treatment 30% O 2 /70% CO 2 at one day of FSP gave the highest value in the overall acceptance characteristic, which was 7.99, while it was found through the results of Figure 4 that the lowest value obtained in control, 30% N 2 /70% CO 2 treatment, and vacuum which were 6.71, 6.60, and 6.71, respectively, in 90 days of FSP.

Conclusions
During this study, a considerable enhancement in the physical properties of the meat treated with MAP was observed. e treatment of 30% N/70% CO 2 showed an improvement in the tenderness property due to an inclined muscle ber index value and a rise in pH. MAP using 15% O 2 /15% N 2 /70% CO 2 gave lower cooking loss than the other treatments. Clove oil gave lower TBA and peroxide values. MAP treatments gave FFAs lower than the control. MAP of 30% O 2 /70% CO 2 gave a higher MFI at all FSPs than other treatments. e di erences between MAP of 30% N 2 /70% CO 2 and 15% O 2 /15% N 2 /70% CO 2 were insigni cant (p < 0.05) and gave a lower liquid loss. In general, cooking loss, TBA, FFAs, and MFI were increased as FSP increased.
e sensory properties of all the MAP and clove oil treatment treatments were improved (took higher scores). e FSP had a signi cant (p < 0.05) in uence on the chemical, physical, and sensory characteristics. MAP treatments have a signi cant e ect on chemical characteristics. e interaction between MAP treatments and FSP signi cantly a ects the physical, chemical, and sensory characteristics. Signi cant advantages of this work are extended shelf life, improved meat quality, and simple design and the workers no need special training to deal with CTMP. Signi cant limitations  Journal of Food Quality are current application is limited for meat and needs special bags. e major attributes of the dataset to decide whether the user is abnormal or normal are lower peroxide value, free fatty acids and TBA, and higher FSP. Future possibilities are manufacturing continuous CTMP or increasing the volume of present CTMP for treatment chicken meat to use in meatprocessing factories. Moreover, for the treatment of other meat such as duck and cow, the application of pulse moderate alternative electric field in CTMP increases its effectiveness.

Data Availability
e dataset used to support the findings of this study is included within the article.

Conflicts of Interest
e authors declare that they have no conflicts of interest.

Authors' Contributions
Asaad R. Al-Hilphy, Majid H. Al-Asadi, Jalilah H. Khalaf, and Amin Mousavi Khaneghah conceptualized the study and contributed to formal analysis, data curation, and writing of the original draft. Muhammad Faisal Manzoor took part in data curation and visualization and revised the original draft.